Mobile communication devices have become increasingly common in current society. The prevalence of these mobile communication devices is driven in part by the many functions that are now enabled on such devices. Increased processing capabilities in such devices means that mobile communication devices have evolved from being pure communication tools into sophisticated mobile multimedia centers that enable enhanced user experiences.
The redefined user experience requires a higher data rate. As such, sophisticated modulation schemes, such as orthogonal frequency division multiplexing (OFDM), are commonly used in mobile communication devices to help improve spectrum efficiency to achieve the higher data rate. In an OFDM-based wireless system, such as long-term evolution (LTE), radio resources are divided into subcarriers in a frequency domain and symbols in a time domain. The subcarriers are orthogonally separated from each other based on a 15 kilohertz (KHz) frequency spacing. The radio resources are allocated to a mobile device in a unit of resource blocks (RBs). According to one of the radio resource allocation schemes in LTE, an RB includes twelve (12) consecutive subcarriers in the frequency domain and seven (7) consecutive OFDM symbols in the time domain. Accordingly, the RB has a bandwidth of 180 KHz (15 KHz/subcarrier×12 subcarriers).
The mobile device may be allocated multiple RBs for communicating a radio frequency (RF) communications signal. In this regard, a bandwidth of the RF communications signal is proportionally related to a number of RBs allocated to the mobile device. For example, if the mobile device is allocated 25 RBs for communicating the RF communications signal, the RF communications signal would occupy a bandwidth of 4.5 megahertz (MHz) (180 KHz/RB×25 RBs). In contrast, if the mobile device were allocated 300 RBs for communicating the RF communications signal, the RF communications signal would occupy a bandwidth of 54 MHz (180 KHz/RB×300 RBs).
Further, to help achieve the higher data rate in the mobile communication devices, sophisticated power amplifiers (PAs) may be employed to increase output power of RF signals (e.g., maintaining sufficient energy per bit) communicated by the mobile communication devices. Envelope tracking is a power management technology designed to improve efficiency levels of the PAs to help reduce power consumption and thermal dissipation in the mobile communication devices. As the name suggests, envelope tracking employs a system that keeps track of the amplitude envelope of the RF signals communicated by the mobile communication devices. The envelope tracking system constantly adjusts a supply voltage applied to the PAs to ensure that the RF PAs are operating at a higher efficiency for a given instantaneous output power requirement of the RF signals.